Plumber's torches are widely used for a soldering or brazing treatment. For more convenience in operation, gas is used instead of some traditional fuels such as benzine and alcohol. The gas is usually accommodated in a metal container of a cassette type, which is commonly and hereinafter named as a cassette, for replacement when being run out of gas. There are two to three sizes of the cassette applicable to a blow torch which has a device for fitting the cassette. A space adjustment device is necessary to a blow torch of such type so as to receive different sizes of the cassette.